The present invention is directed to apparatuses and methods for monitoring parameters in devices. The present invention is especially useful in battery monitoring circuits for monitoring charge levels in battery devices.
By way of example and not by way of limitation, the present invention will be described in an exemplary embodiment of an apparatus and method for monitoring charge level in a battery device. The teachings of the present invention apply generally to any arrangement for monitoring a parameter in a host device where the parameter can be represented by an indicator signal, such as by an indicator voltage signal.
Presently available devices for monitoring charge level in a battery device (sometimes referred to as xe2x80x9cgas gaugesxe2x80x9d) are generally accurate for coulomb counting in carrying out battery monitoring operations. One important parameter that affects coulomb counting accuracy is the device input offset. Further, input offset may vary, or drift, with changes in temperature or applied supply power. In today""s market smaller sizes of devices and lower operating voltages are increasingly prevalent with a result that sense elements in battery packs for sensing charge levels are smaller and power dissipation in portable electronic devices is reduced. These changes make accurate xe2x80x9cgas gaugingxe2x80x9d or charge monitoring increasingly difficult, especially when the offset experienced by a monitoring circuit or apparatus is of the same order of magnitude as the standby voltage developed across the sense resistor used to generate a representative voltage for effecting charge monitoring. Challenges in accurate charge monitoring further increase when the monitoring apparatus offset drifts with temperature, or applied supply voltage, or another factor.
Prior art solutions for accommodating or allowing for offset cancellation have been based upon an offset value that is measured one time at a particular extant temperature and supply voltage. Such a static determination of offset at fixed temperature and supply voltage values for use throughout an operational period for a monitoring apparatus does not permit accurate accommodation for offset based upon realistic and up to date evaluations of currently extant conditions affecting offset as the host device and monitoring apparatus operate. Accordingly, offset values may approach levels that significantly exceed allowances made for the offset (based upon once-determined measurements) and thereby cause inaccuracies in indications by a monitoring circuit.
There is a need for an apparatus and method for determining offset cancellation that permits realistic accommodation of currently extant factors affecting offset over time.
An apparatus receives an indicating signal representing a parameter at a monitoring locus and includes: (a) A first measuring unit having a first input coupled for selectively receiving the indicating signal and presenting a first output signal that includes a first monitoring signal representing change in the indicating signal during a first time interval and a first benchmark signal indicating change imparted to signals by the first measuring unit. (b) A second measuring unit having a second input coupled for selectively receiving the indicating signal and presenting a second output signal that includes a second monitoring signal representing change in the indicating signal during a second time interval and a second benchmark signal indicating change imparted to signals by the second measuring unit. (c) An accumulating unit coupled for receiving and evaluating the first and second output signals and generating an accumulated signal that represents the evaluating. (d) An indicator unit coupled with the accumulating unit for receiving the indicator signal and presenting an indication relating to excursion of the indicating signal.
A method for measuring a parameter in a host device providing an indicating signal representative of the parameter at a signal monitoring locus includes the steps of: (a) in no particular order: (1) providing a first voltage measuring unit having a first input locus and a first output locus; (2) providing a second voltage measuring unit having a second input locus and a second output locus; (3) providing an accumulating unit coupled with the first output locus and the second output locus; the accumulating unit having at least one accumulated indicator output locus; and (4) providing an indicator unit coupled with the at least one accumulated indicator output locus. (b) Coupling the first input locus with the monitoring locus, and coupling the second input locus with ground during a first time interval. The first voltage measuring unit receives the indicating signal at the first input locus and presents a first monitoring signal at the first output locus. The second voltage measuring unit presents a second benchmark signal at the second output locus. The first monitoring signal represents change in the indicating signal during the first time interval. The second benchmark signal indicates changes imparted to signals by the second voltage measuring unit when traversing the second voltage measuring unit during the first time interval. (c) Coupling the second input locus with the monitoring locus, and coupling the first input locus with ground during a second time interval. The second voltage measuring unit receives the indicating signal at the second input locus and presents a second monitoring signal at the second output locus. The first voltage measuring unit presents a first benchmark signal at the first output locus. The second monitoring signal represents change in the indicating signal during the second time interval. The first benchmark signal indicates changes imparted to signals by the first voltage measuring unit when traversing the first voltage measuring unit during the second time interval. (d) Operating the accumulating unit to receive the first output signal and the second output signal, to evaluate the first output signal and the second output signal and to generate at least one accumulated indicator signal at the at least one accumulated indicator output locus. The at least one accumulated indicator signal represents the evaluating. (e) Operating the indicator unit to receive the at least one accumulated indicator signal and present an indication relating to excursion of the indicating signal.
It is, therefore, an object of the present invention to provide an apparatus and method for measuring a parameter in a host device that permits realistic accommodation of currently extant factors affecting offset to facilitate accurate determination of offset cancellation.
Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the invention.